Circular Dischroism Research Articles

Five Tetramic Acid Derivatives Isolated from the Iranian Fungus Colpomaquercinum CCTU A372.

Submerged mycelial cultures of the ascomycete Colpoma quercinum CCTU A372 were found to produce five previously undescribed tetramic acids, for which we propose the trivial names colposetins A–C (1–3) and colpomenoic acids A and B (4 and 5), along with the known compounds penicillide (6) and monodictyphenone (7). The planar structures of 1–5 were determined by high-resolution electrospray ionization mass spectrometry (HR-ESIMS) and extensive 1D and 2D nuclear magnetic resonance (NMR) spectroscopy. Their absolute configurations were determined by the combination of electronic circular dischroism (ECD) analysis, J-based configurational analysis, and a rotating-frame Overhauser effect spectroscopy (ROESY) experiment. Colposetin B displayed weak antimicrobial activity against Bacillus subtilis and Mucor hiemalis (MIC 67 µg/mL).

Redox and optically active carbohelicene layers prepared by potentiodynamic polymerization

This short paper describes the preparation of thin layers based on carbohelicenes, which are inherently chiral polyaromatics existing in the enantiomeric forms P and M. Specifically, [5]-, [6]- and [7]helicene were subjected to redox cycling between −1.5 and 1.5 V vs. ferrocene/ferrocenium at a scan rate of 10 V/s. This way, enantiopure layers exhibiting redox activity were formed on the surfaces of the glassy carbon and ITO electrodes under anoxic and non-aqueous conditions. The properties of the prepared polymer layers were investigated using electrochemistry with Fe/Ru redox probes, circular dischroism, AFM, impedance measurement and Raman spectroscopy. With [6]helicene, the suggested electropolymerization procedure thus represents a proof-of-concept for the preparation of chiral carbonaceous surfaces.

The Study of the Interaction between Doxorubicin and Single‐Stranded DNA

AbstractThe binding properties of doxorubicin with single stranded DNA of various base compositions were determined by fluorescence and circular dischroism assays. The interaction of Dox with ssDNA comprising of single repeating deoxynucleotide was firstly investigated. Dox preferentially bound to the G residues among four bases. Then oligonucleotides covering potential GA, GT, GC or GG binding sites were designed to quantitatively analyze the preferential base composition at the binding site. Dox exhibited better effect on oligonucleotide with GC sites. To testify the binding preference to GC site, GC‐rich oligonucleotides containing two GC fragments with different array modes were employed. Dox was verified to preferentially bind to the GC site of single stranded DNA. The binding of Dox with GC site in single stranded DNA may involve in the cooperation interaction of multiple GC with one Dox molecule. It appears that Dox may prefer stacking interaction with the multiple GC nucleotide bases along the oligonucleotide backbone.

Violation of Hund's third rule in structurally disordered ferromagnets

Violation of Hund’s third rule caused by structural disorder is observed for the induced magnetic moment of Zr, using X-ray magnetic circular dischroism. The induced spin and orbital magnetic momen ...

Interaction of Jatrorrhizine with Human Gamma Globulin in membrane mimetic environments: Probing of the binding mechanism and binding site by spectroscopic and molecular modeling methods

The interaction between Jatrorrhizine and Human Gamma Globulin (HGG) in AOT/isooctane/water microemulsions was studied by using fluorescence quenching, UV absorption spectroscopy, circular dischroism (CD) spectroscopy and dynamic light scattering (DLS). Fluorescence data in water-surfactant molar ratio ( ω 0) 25 microemulsions revealed the presence of the binding site of Jatrorrhizine on HGG and its binding constants at four temperatures were obtained. The affinities in microemulsions were similar to that in buffer solution. The alterations of ΗGG secondary structure in the microemulsions in the absence and presence of Jatrorrhizine compared with the free form of HGG in buffer were analyzed by CD spectroscopy. In addition, the DLS data suggested that HGG may locate inside the microemulsion and Jatrorrhizine could interact with them. Furthermore, the thermodynamic functions, i.e. standard enthalpy ( Δ H 0 ) and standard entropy ( Δ S 0 ) for the reaction were also calculated, according to Van’t Hoff equation. These data showed that hydrophobic and electrostatic interaction played the main role in the binding of Jatrorrhizine to HGG.

High-yield production, refolding and a molecular modelling of the catalytic module of (1,3)-β-d-glucan (curdlan) synthase from Agrobacterium sp.

Biosynthesis of the (1,3)-beta-D: -glucan (curdlan) in Agrobacterium sp., is believed to proceed by the repetitive addition of glucosyl residues from UDP-glucose by a membrane-embedded curdlan synthase (CrdS) [UDP-glucose: (1,3)-beta-D: -glucan 3-beta-D: -glucosyltransferase; EC 2.4.1.34]. The catalytic module of CrdS (cm-CrdS) was expressed in good yield from a cDNA encoding cm-CrdS cloned into the pET-32a(+) vector, containing a coding region for thioredoxin, and from the Champion pET SUMO system that possesses a coding region of a small ubiquitin-related modifier (SUMO) partner protein. The two DNA fusions, designated pET-32a_cm-CrdS and SUMO_cm-CrdS were expressed as chimeric proteins. High yields of inclusion bodies were produced in E. coli and these could be refolded to form soluble proteins, using a range of buffers and non-detergent sulfobetaines. A purification protocol was developed, which afforded a one-step on-column refolding and simultaneous purification of the recombinant 6xHis-tagged SUMO_cm-CrdS protein. The latter protein was digested by a specific protease to yield intact cm-CrdS in high yields. The refolded SUMO_cm-CrdS protein did not exhibit curdlan synthase activity, but showed a circular dischroism spectrum, which had an alpha/beta-type-like conformation. Amino acid sequences of tryptic fragments of the SUMO_cm-CrdS fusion and free cm-CrdS proteins, determined by MALDI/TOF confirmed that the full-length proteins were synthesized by E. coli, and that no alterations in amino acid sequences occurred. A three-dimensional model of cm-CrdS predicted the juxtaposition of highly conserved aspartates D156, D208, D210 and D304, and the QRTRW motif, which are likely to play roles in donor and acceptor substrate binding and catalysis.

Cloning, expression, secondary structure characterization of HMG box 1 of hUBF from E. coli and its binding to DNA

Human upstream binding factor (hUBF) belonging to a family of protein containing DNA binding domain-HMG box, is important in the activation of rRNA gene transcription. It contains six tandemly arranged HMG box domains, each of which is thought to be as a basic architectural unit in the interaction of DNA and protein. Here the DNA binding domain of hUBF HMG box 1 was cloned and heterologously expressed in Escherichia coli. Through a single purification step using a Ni 2+-chelating column, the highly purified recombinant protein could be obtained. This recombinant protein contains 99 amino acids with a hexahistidine tag added to the C-terminus. It was expressed as a monomer, which was determined by gel filtration. Circular dischroism studies show that it comprises approximately 54.3% α-helix and 43.6% random coil at pH 7. This result is in good agreement with that of FTIR, which are 59.9% α-helix and 40.1% random coil. There is no obvious change for the secondary structure of the recombinant protein as increasing pH from 5.0 to 12.0. But denaturation occurs at pH 3.0. Like many HMG box domains that were found in other proteins, it could bind to four-way DNA junction, a putative intermediate in DNA recombination, in a structure-specific manner. Magnesium ion has no effect on this binding activity, which is determined by both gel mobility shift assays and surface plasmon resonance (SPR). Since Mg 2+ is present in the nucleus and RNA polymerase I is Mg 2+-stimulated, we believe that this property is relevant for hUBF in vivo. SPR research shows that the recombinant hUBF HMG box 1 also has a strong binding ability to a GC-rich fragment within the rRNA gene core promoter.

Conformational flexibility of three cytoplasmic segments of the angiotensin II AT1A receptor: a circular dichroism and fluorescence spectroscopy study.

The conformation of three synthetic peptides encompassing the proximal and distal half of the third intracellular loop (Ni3 and Ci3) and a portion of the cytoplasmic tail (fCT) of the angiotensin II AT1A receptor has been studied using circular dischroism and fluorescence spectroscopies. The results show that the conformation of the peptides is modulated in various ways by the environmental conditions (pH, ionic strength and dielectric constant). Indeed, Ni3 and fCT fold into helical structures that possess distinct stability and polarity due to the diverse forces involved: mainly polar interactions in the first case and a combination of polar and hydrophobic interactions in the second. The presence of these various features also produce distinct intermolecular interactions. Ci3, instead, exists as an ensemble of partially folded states in equilibrium. Since the corresponding regions of the angiotensin II AT1A receptor are known to play an important role in the receptor function, due to their ability to undergo conformational changes, these data provide some new clues about their different conformational plasticity.

Time-Resolved Profiles in Modulated Polarization Spectroscopy

The absorption of a modulated light beam in which the state of the polarization is continuously variable is discussed. It is now possible to measure the average time-dependent profile for the polarization cycle of such a beam, and corresponding theoretical descriptions are needed in order to extract the information contained in it. This work generates such a description. Based on a semiclassical treatment of light/matter interactions, a three-parameter fit function is derived that permits the simultaneous extraction of absorbance, linear dichroism, and circular dischroism from the profile for various types of uniformly oriented, partially oriented, and isotropic materials and combinations of them. The theoretical expressions are used to analyze data for (+)-3-methylcyclopentanone, the results being (1) an increase of the S/N ratio, (2) the simultaneous generation of absorption and dichroism spectra of identical quality, and (3) a description of window adsorbates of the cyclopentanone material. The Jones parameters for the macroscopic description of polarized light interactions with matter are reformulated at the microscopic (i.e., transition moment) level, and an alternative derivation of the Jones matrix is given.

Interfacial effects in Fe/4d TM multilayers (abstract)

We have studied Fe/TM multilayers (TM=Mo, Nb, Ru, Rh, Pd) using x-ray magnetic circular dischroism, magneto-optical Kerr effect, and x-ray diffraction. A diverse set of magnetic behaviors emerges from the analysis. We focus on the behavior which can be attributed to the existence of a physical interface between different chemical species. In particular, we have measured an enhanced Fe moment in some cases (TM=Ru, Mo, Rh, Pd) yet not in others (TM=Nb). These results will be discussed, including the relative orbital and spin moments and the effects of alloying at the interface. The measured induced moments in the TM layer will be presented as well where applicable.

A high-purity circular polarization modulator: Application to birefringence and circular dichroism measurements on multidielectric mirrors

We present a method for producing a modulated circular polarization of high purity, i.e. whose modulation frequency allows specific discrimination against linear polarization and unpolarized intensity. We apply it to measure the circular dischroism and birefringence of high reflectivity multidielectric mirrors: no circular dichroism is observed at a level of 10 −6, but birefringence values from 3 x 10 −4 to 2 x 10 −3 radian per reflexion under normal incidence are obtained.

Reactivity of the antibodies to DNA modified by the carcinogen N-acetoxy-N-acetyl-2-aminofluorene.

Rabbits were immunized with native DNA modified by the carcinogen N-acetoxy-N-acetyl-2-aminofluorene. The interactions between the purified antibodies to nDNA-AAF (or the Fab fragments) and several ligands have been studied. By radioimmunoassay, nDNA-AAF, dDNA-AAF, and GMP-AAF were found to bind to the antibodies with about the same affinity. GMP-AF interacts slightly less, and GMP and N-OH-AAF do not interact. The values of the association constants deduced from fluorescence measurements for the binding of the Fab fragments to nDNA-AAF, dDNA-AAF, and GMP-AAF, in 50 mM NaCl, pH 7.5, are of the same order of magnitude. The values of the association constants with nDNA-AAF and dDNA-AAF depend upon salt concentration. From this variation; it is deduced that 1-1.5 phosphate groups interact by charge--charge interactions with the Fab fragments. The absorption and circular dischroism spectra of GMP-AAF, nDNA-AAF, and dDNA-AAF bound to the Fab fragments show that the Fab fragments induce similar perturbation to the three ligands. These results lead to the conclusion that the immunodeterminant group is the dGMP-AAF residue.

Resistance of lipophilin, a hydrophobic myelin protein, to denaturation by urea and guanidinium salts.

The influence of urea, guanidinium chloride (GdmCl), and granidinium thiocyanate (GdmSCN) on the solution structure of lipophilin was examined by circular dischroism and fluorescence techniques. According to the CD results, lipophilin retained at least 60% of organized secondary structure in 8 M urea and 6 M GdmCl (measurements were not possible in GdmSCN). This partial denaturation was of a complex, irreversible nature, and was not appreciably enhanced by prolonged incubation (8 days), by heating to 70 degrees C, by disulfide bond reduction, or by pH variation in the range pH 1.5 to 11. Fluorescence studies demonstrated that the tryptophan residues were only slightly perturbed by 8 M and 6 M GdmCl and remained well buried to the permeant quenching agent acrylamide. A greater, but still far from complete, disruption of lipophilin was achieved in 6 M GdmSCN, and fluorescence polarization provided evidence for some form of cooperative structural change induced by increasing concentrations of this reagent. Transfer of the protein from 2-chloroethanol, in which the tryptophan residues are fully exposed, into 6 M GdmSCN by dialysis resulted in reburial of the fluorophores owing to development of tertiary structure. The combined evidence suggests that the extraordinary resistance of lipophilin to these denaturants is due to the presence of an impervious hydrophobic core. In lipophilin and some other membrane-associated proteins, extended sequences of apolar residues might provide the nuclei for such structural domains.

Circular dichroism investigation of the (L Lysine) n-Cu(II) (I:I) System with n = 4 and n = 25

The study of the (L Lysine) n -Cu(II) (I:I) system with n = 4 and n = 25 using circular dischroism (CD) data has provided evidence indicating the formation of two complexes in a two-atep process. In the first of these complexes, obtained at pH 6.6 the α-amino terminal group and the adjacent deprotonated amide nitrogen are bound to the metal. In the second, additional amino nitrogens of side chains lie at the other two corners of the coordination square.A comprehensive investigation of changes occuring in special patterns when coordination takes place enables the assignment of three bands that are characteristic to each type of nitrogen coordination.

Vibrational circular dichroism of overtone and combination bands

Vibrational circular dischroism (VCD) is reported in overtone and combination bands of chiral molecules in solution.

Absorptive and scattering circular dischroism of cholesteric liquid crystals in the infrared

The infrared circular dichroism (IRCD) of chloesteric liquid crystals prepared from nematic material doped with varing amounts of optically-active compounds has been measured. Large, narrow circular dichroism (CD) bands arising from molecular vibrations in the helical array can be distinguished from the CD of the broad cholestric reflection bands.

Optical rotatory dispersion and circular dichroic spectra of G-actin

Optical rotatory dispersion and circular dichroic spectra of native G-actin containing either Mg 2+, Ca 2+, or Mn 2+ as the strongly bound cation did not differ in the far ultraviolet. Similarly, exchange of the bound ATP for ITP did not affect the peptide backbone conformation of the protein. Denaturation by heat or EDTA caused an irreversible loss of about 40% of the optically active structure of G-actin. From the ultraviolet circular dichroic spectra the conclusion was drawn that α-helix is the main optically active conformation both in the native and denatured actin and amounts to about 30% and 18%, respectively. The contribution of the β structure may not exceed 10%, while the remaining residues do not appear to contribute to the optical activity. Indications by circular dischroism of the presence of unfolded coil structures appear only in 6 m guanidine HCl. Sucrose, 30%, has no effect on the circular dichroic values of native G-actin, but it causes a reversible increase in circular dichroic values of denatured actin. Certain features of the circular dichroic pattern are consistent with there being rather short helical segments in actin.

Circular dischroism of Japanese-radish peroxidase a.

Circular dischroism of Japanese-radish peroxidase a.